Magnetic field generator for a magnetic field measurement system

ABSTRACT

A magnetic field generator includes a first planar substrate, a second planar substrate positioned opposite to the first planar substrate and separated from the first planar substrate by a gap, a first wiring set on the first planar substrate, a second wiring set on the second planar substrate, and one or more interconnects between the first planar substrate and the second planar substrate. The one or more interconnects electrically connect the first wiring set with the second wiring set to form a continuous electrical path. The continuous electrical path forms a conductive winding configured to generate, when supplied with a drive current, a first component of a compensation magnetic field configured to actively shield a magnetic field sensing region located in the gap from ambient background magnetic fields along a first axis that is substantially parallel to the first planar substrate and the second planar substrate.

RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. § 119(e) to U.S.Provisional Patent Application No. 62/842,818, filed on May 3, 2019, andto U.S. Provisional Patent Application No. 62/933,160, filed on Nov. 8,2019, and to U.S. Provisional Patent Application No. 62/933,167, filedon Nov. 8, 2019, and to U.S. Provisional Patent Application No.62/933,169, filed on Nov. 8, 2019, and to U.S. Provisional PatentApplication No. 62/933,170, filed on Nov. 8, 2019, and to U.S.Provisional Patent Application No. 62/933,287, filed on Nov. 8, 2019,and to U.S. Provisional Patent Application No. 62/933,288, filed on Nov.8, 2019, and to U.S. Provisional Patent Application No. 62/933,289,filed on Nov. 8, 2019, and to U.S. Provisional Patent Application No.62/933,174, filed on Nov. 8, 2019, and to U.S. Provisional PatentApplication No. 62/967,787, filed on Jan. 30, 2020, and to U.S.Provisional Patent Application No. 62/967,797, filed on Jan. 30, 2020,and to U.S. Provisional Patent Application No. 62/967,803, filed on Jan.30, 2020, and to U.S. Provisional Patent Application No. 62/967,804,filed on Jan. 30, 2020, and to U.S. Provisional Patent Application No.62/967,813, filed on Jan. 30, 2020, and to U.S. Provisional PatentApplication No. 62/967,818, filed on Jan. 30, 2020, and to U.S.Provisional Patent Application No. 62/967,823, filed on Jan. 30, 2020.These applications are incorporated herein by reference in theirrespective entireties.

BACKGROUND INFORMATION

Optical magnetometry is the use of optical methods to measure a magneticfield with very high accuracy. An optically pumped magnetometer (OPM) isa fundamental element used in optical magnetometry to measure magneticfields. Of particular interest for their high-sensitivity, OPMs can beused in optical magnetometry to measure weak magnetic fields, such asmagnetic fields generated by the brain. For example, spin-exchangerelaxation-free (SERF) mode OPMs can achieve femto-Tesla (fT)/(Hz)^(1/2)sensitivities. However, the OPMs may also sense ambient magnetic fieldsassociated with sources other than the magnetic field measurement systemand the source(s) of interest (e.g., neural signals from a user'sbrain). For example, SERF mode OPMs can also sense the Earth's magneticfield (which is about 50 μT), as well as magnetic fields from magnets,electromagnets, electrical devices, and other signal or field generatorsin the environment.

To use a SERF mode OPM outside a shielded room, an active magnetic fieldshield can be used. An active magnetic field shield generates, forexample, an equal and opposite magnetic vector that cancels out, orsubstantially reduces, the ambient magnetic field, including the Earth'smagnetic field. However, active magnetic field shields are not presentlysuitable to be worn by a user due at least to their large size and themobility constraints they impose upon the user.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate various embodiments and are a partof the specification. The illustrated embodiments are merely examplesand do not limit the scope of the disclosure. Throughout the drawings,identical or similar reference numbers designate identical or similarelements. Furthermore, the figures are not necessarily drawn to scale asone or more elements shown in the figures may be enlarged or resized tofacilitate recognition and discussion.

FIG. 1 illustrates an exemplary magnetic field measurement systemaccording to principles described herein.

FIG. 2 illustrates an exemplary computing device that may implement acontroller of the magnetic field measurement system of FIG. 1 accordingto principles described herein.

FIG. 3 illustrates an exemplary configuration of the magnetic fieldmeasurement system of FIG. 1 according to principles described herein.

FIG. 4 illustrates another exemplary configuration of the magnetic fieldmeasurement system of FIG. 1 according to principles described herein.

FIG. 5 illustrates yet another exemplary configuration of the magneticfield measurement system of FIG. 1 according to principles describedherein.

FIG. 6 illustrates a block diagram of an exemplary magnetometeraccording to principles described herein.

FIG. 7 shows a magnetic spectrum in magnetic field strength on alogarithmic scale according to principles described herein.

FIG. 8A illustrates an exemplary Bz′ component generator of a magneticfield generator according to principles described herein.

FIG. 8B illustrates an exemplary configuration of the Bz′ componentgenerator of FIG. 8A.

FIGS. 9A-9D illustrate exemplary functional diagrams of variousconfigurations of the Bz′ component generator of FIG. 8A according toprinciples described herein.

FIG. 10 illustrates another exemplary Bz′ component generator of amagnetic field generator according to principles described herein.

FIG. 11A illustrates a functional diagram of an exemplary configurationof the Bz′ component generator of FIG. 10 according to principlesdescribed herein.

FIG. 11B illustrates an exemplary configuration of the Bz′ componentgenerator 800 of FIGS. 10 and 11A according to principles describedherein.

FIG. 12 illustrates an exemplary functional diagram for driving a Bz′component generator according to principles described herein.

FIG. 13 illustrates another exemplary functional diagram for driving aBz′ component generator according to principles described herein.

FIGS. 14A and 14B show plan views of an exemplary Bx′/By′ componentgenerator according to principles described herein.

FIG. 14C shows a side view functional diagram of the Bx′/By′ componentgenerator of FIGS. 14A and 14B taken along the dashed lines labeledXIV-XIV according to principles described herein.

FIGS. 15A and 15B illustrate exemplary configurations of an elastomericconnector that may be used as interconnects in the Bx′/By′ componentgenerator of FIGS. 14A-14C according to principles described herein.

FIGS. 16A and 16B show plan views of another exemplary Bx′/By′ componentgenerator according to principles described herein.

FIG. 16C shows a side view functional diagram of the Bx′/By′ componentgenerator of FIGS. 16A and 16B taken along the dashed lines labeledXVI-XVI according to principles described herein.

FIGS. 17A and 17B show plan views of another exemplary Bx′/By′ componentgenerator according to principles described herein.

FIG. 17C shows a side view functional diagram of the Bx′/By′ componentgenerator of FIGS. 17A and 17B taken along the dashed lines labeledXVII-XVII according to principles described herein.

FIGS. 18A and 18B show plan views of an exemplary configuration of aBx′/By′ component generator according to principles described herein.

FIG. 18C shows a perspective view of various conductive windings thatmay be included in the Bx′/By′ component generator of FIGS. 18A and 18Baccording to principles described herein.

FIG. 19 shows a perspective view of an exemplary physical implementationof a wearable sensor unit according to principles described herein.

FIG. 20 shows a cross-sectional side view of the physical implementationof the wearable sensor unit shown in FIG. 19 according to principlesdescribed herein.

FIGS. 21A-21C show functional diagrams of exemplary wearable devicesaccording to principles described herein.

FIGS. 22-27 illustrate exemplary physical implementations of a wearabledevice 2200 according to principles described herein.

FIG. 28 illustrates an exemplary magnetic field generator design systemaccording to principles described herein.

FIGS. 29-32 illustrate exemplary methods of making a magnetic fieldgenerator according to principles described herein.

FIG. 33 illustrates an exemplary computing device according toprinciples described herein.

DETAILED DESCRIPTION

Magnetic field generators for use in magnetic field measuring systemsare described herein. An exemplary magnetic field generator includes afirst planar substrate, a second planar substrate positioned opposite tothe first planar substrate and separated from the first planar substrateby a gap, a first wiring set disposed on the first planar substrate, asecond wiring set disposed on the second planar substrate, and one ormore interconnects positioned between the first planar substrate and thesecond planar substrate. The one or more interconnects electricallyconnect the first wiring set with the second wiring set to form a firstcontinuous electrical path. The first continuous electrical path forms afirst conductive winding configured to generate, when supplied with adrive current, a first component of a compensation magnetic field (e.g.,Bx′ component or a By′ component) configured to actively shield amagnetic field sensing region located in the gap from ambient backgroundmagnetic fields along a first axis that is substantially parallel to thefirst planar substrate and the second planar substrate. For example, thefirst component of the compensation magnetic field may reduce or cancela first component (e.g., a Bx component or a By component) of theambient background magnetic field, which is the component of the ambientbackground magnetic field along the first axis. In some examples thefirst component of the compensation magnetic field is substantiallyequal and opposite to the first component of the ambient backgroundmagnetic field.

In some examples, a wearable sensor unit may include a plurality ofmagnetometers and a magnetic field generator. The plurality ofmagnetometers (e.g., vapor cells included in the plurality ofmagnetometers) may be positioned in the magnetic field sensing region.Accordingly, the magnetic field generator may generate a magnetic fieldconfigured to actively shield the magnetometers (e.g., the vapor cells)from the first component of the ambient background magnetic field.

Advantageously, the magnetic field generators described hereinsubstantially reduce or cancel a first component of the ambientbackground magnetic field in a magnetic field sensing region withminimal spatial variability. For example, the ambient backgroundmagnetic field may vary by no more than 10-20 nano-Tesla (nT) within themagnetic field sensing region. Additionally, the magnetic fieldgenerators may be much smaller compared to conventional configurations.For example, the magnetic field generators (e.g., the conductivewindings and/or substrates on which the conductive windings arearranged) may be approximately three-and-a-half (3.5) times, or less,than the size of the magnetic field sensing region when measured alongan axis that is orthogonal to the first axis (e.g., an x-axis or ay-axis). Accordingly, the magnetic field generator can be easilyintegrated into a wearable sensor unit that may be worn (e.g., on ahead) by a user. Thus, the magnetic field generators described hereinmay allow for greater mobility of a user wearing the wearable sensorunit(s). Additionally, multiple wearable sensor units may be included ina wearable device of a magnetic field measurement system, therebyallowing high resolution magnetic field measurement. Furthermore, themagnetic field generator described herein can be easily manufacturedwith a simple process. These and other benefits will be made apparent inthe disclosure that follows.

FIG. 1 shows an exemplary magnetic field measurement system 100 (“system100”). As shown, system 100 includes a wearable sensor unit 102 and acontroller 104. Wearable sensor unit 102 includes a plurality ofmagnetometers 106-1 through 106-N (collectively “magnetometers 106”) anda magnetic field generator 108. Wearable sensor unit 102 may includeadditional components (e.g., one or more magnetic field sensors,position sensors, orientation sensors, accelerometers, image recorders,detectors, etc.) as may serve a particular implementation. System 100may be used in MEG and/or any other application that measures relativelyweak magnetic fields.

Wearable sensor unit 102 is configured to be worn by a user (e.g., on ahead of the user). In some examples, wearable sensor unit 102 isportable. In other words, wearable sensor unit 102 may be small andlight enough to be easily carried by a user and/or worn by the userwhile the user moves around and/or otherwise performs daily activities.

Any suitable number of magnetometers 106 may be included in wearablesensor unit 102. For example, wearable sensor unit 102 may include anarray of nine, sixteen, twenty-five, or any other suitable plurality ofmagnetometers 106 as may serve a particular implementation.

Magnetometers 106 may each be implemented by any suitable combination ofcomponents configured to be sensitive enough to detect a relatively weakmagnetic field (e.g., magnetic fields that come from the brain). Forexample, each magnetometer may include a light source, a vapor cell suchas an alkali metal vapor cell (the terms “cell,” “gas cell,” “vaporcell,” and “vapor gas cell” are used interchangeably herein), a heaterfor the vapor cell, and a photodetector (e.g., a signal photodiode).Examples of suitable light sources include, but are not limited to, adiode laser (such as a vertical-cavity surface-emitting laser (VCSEL),distributed Bragg reflector laser (DBR), or distributed feedback laser(DFB)), light-emitting diode (LED), lamp, or any other suitable lightsource. In some embodiments, the light source may include two lightsources: a pump light source and a probe light source. Thesemagnetometer components, and manners in which they operate to detectmagnetic fields, are described in more detail herein, as well as in inco-pending U.S. patent application Ser. No. 16/457,655, filed Jun. 28,2019, which application is incorporated by reference herein in itsentirety.

Magnetic field generator 108 may be implemented by one or morecomponents configured to generate one or more compensation magneticfields that actively shield magnetometers 106 (including respectivevapor cells) from ambient background magnetic fields (e.g., the Earth'smagnetic field, magnetic fields generated by nearby magnetic objectssuch as passing vehicles, electrical devices and/or other fieldgenerators within an environment of magnetometers 106, and/or magneticfields generated by other external sources). For example, magnetic fieldgenerator 108 may be configured to generate compensation magnetic fieldsin the x-, y-, and/or z-direction (all directions are with respect toone or more planes within which magnetic field generator 108 islocated). The compensation magnetic fields are configured to cancel out,or substantially reduce, ambient background magnetic fields in amagnetic field sensing region with minimal spatial variability. As usedherein, magnetic fields generated by magnetic field generator 108 in thez-direction are referred to as a Bz′ component of the compensationmagnetic field, magnetic fields generated by magnetic field generator108 in the x-direction are referred to as a Bx′ component of thecompensation magnetic field, and magnetic fields generated by magneticfield generator 108 in the y-direction are referred to as a By′component of the compensation magnetic field. Specific implementationsof magnetic field generator 108 are described in more detail herein.

Controller 104 is configured to interface with (e.g., control anoperation of, receive signals from, etc.) magnetometers 106 and themagnetic field generator 108. Controller 104 may also interface withother components that may be included in wearable sensor unit 102 (e.g.,magnetic field sensors).

In some examples, controller 104 is referred to herein as a “single”controller 104. This means that only one controller is used to interfacewith all of the components of wearable sensor unit 102. For example,controller 104 is the only controller that interfaces with magnetometers106 and magnetic field generator 108. This is in contrast toconventional configurations in which discrete magnetometers each havetheir own discrete controller associated therewith. It will berecognized, however, that any number of controllers may interface withcomponents of magnetic field measurement system 100 as may suit aparticular implementation.

As shown, controller 104 may be communicatively coupled to each ofmagnetometers 106 and magnetic field generator 108. For example, FIG. 1shows that controller 104 is communicatively coupled to magnetometer106-1 by way of communication link 110-1, to magnetometer 106-2 by wayof communication link 110-2, to magnetometer 106-N by way ofcommunication link 110-N, and to magnetic field generator 108 by way ofcommunication link 112. In this configuration, controller 104 mayinterface with magnetometers 106 by way of communication links 110-1through 110-N (collectively “communication links 110”) and with magneticfield generator 108 by way of communication link 112.

Communication links 110 and communication link 112 may be implemented byany suitable wired connection as may serve a particular implementation.For example, communication links 110 may be implemented by one or moretwisted pair cables while communication link 112 may be implemented byone or more coaxial cables. Other communication links between controller104 and wearable sensor unit 102 may additionally be included tofacilitate control of and/or communication with other componentsincluded in wearable sensor unit 102.

Controller 104 may be implemented in any suitable manner. For example,controller 104 may be implemented by a field-programmable gate array(FPGA), an application specific integrated circuit (ASIC), a digitalsignal processor (DSP), a microcontroller, and/or other suitable circuittogether with various control circuitry.

In some examples, controller 104 is implemented on one or more printedcircuit boards (PCBs) included in a single housing. In cases wherecontroller 104 is implemented on a PCB, the PCB may include variousconnection interfaces configured to facilitate communication links 110and 112. For example, the PCB may include one or more twisted pair cableconnection interfaces to which one or more twisted pair cables may beconnected (e.g., plugged into) and/or one or more coaxial cableconnection interfaces to which one or more coaxial cables may beconnected (e.g., plugged into).

In some examples, controller 104 may be implemented by or within acomputing device. FIG. 2 illustrates an exemplary computing device 200that may implement controller 104. Computing device 200 may beimplemented by a desktop computer, a mobile device, a server, and/or anyother single computing device having a single housing for components ofthe computing device.

As shown, computing device 200 may include, without limitation, astorage facility 202 and a processing facility 204 selectively andcommunicatively coupled to one another. Facilities 202 and 204 may eachinclude or be implemented by hardware and/or software components (e.g.,processors, memories, communication interfaces, instructions stored inmemory for execution by the processors, etc.).

Storage facility 202 may maintain (e.g., store) executable data used byprocessing facility 204 to perform one or more of the operationsdescribed herein. For example, storage facility 202 may storeinstructions 206 that may be executed by processing facility 204 toperform one or more of the operations described herein. Instructions 206may be implemented by any suitable application, software, code, and/orother executable data instance. Storage facility 202 may also maintainany data received, generated, managed, used, and/or transmitted byprocessing facility 204.

Processing facility 204 may be configured to perform (e.g., executeinstructions 206 stored in storage facility 202 to perform) variousoperations described herein.

As shown, computing device 200 may be communicatively coupled to a userinput device 208 and to a display device 210. User input device 208 maybe implemented by a keyboard, a mouse, a touch screen, a track ball, ajoystick, a voice recognition system, and/or any other componentconfigured to facilitate providing of user input to computing device200. Display device 210 may be implemented by a monitor, a screen, aprinter, and/or any other device configured to display output providedby computing device 200. In some examples, display device 210 isintegrated into a single unit with computing device 200.

FIG. 3 illustrates an exemplary configuration 300 of system 100 in whichcontroller 104 includes a clock source 302 configured to generate acommon clock signal used by controller 104 to interface with thecomponents of wearable sensor unit 102. For example, controller 104 mayuse the common clock signal to drive or otherwise control variouscomponents within each of magnetometers 106 and drive or otherwisecontrol magnetic field generator 108. Use of the common clock signal tointerface with magnetometers 106 and magnetic field generator 108 isillustrated in FIG. 3 (and various other figures) by dashed linesinterconnecting clock source 302 and magnetometers 106 and magneticfield generator 108.

By using a single common clock signal (as opposed to an array ofindependent clocks as done in conventional configurations), controller104 may ensure that communication with magnetometers 106 and magneticfield generator 108 (and, in some implementations, other componentswithin wearable sensor unit 102) is synchronized, thereby reducing oreliminating crosstalk between signals transmitted between controller 104and wearable sensor unit 102, as well as providing other benefitsdescribed herein.

In some implementations, as illustrated in FIGS. 1 and 3, controller 104is remote from (i.e., not included within) wearable sensor unit 102. Forexample, in these implementations, controller 104 may be implemented byor included in a standalone computing device not configured to be wornby a user (e.g., computing device 200). The computing device mayinterface with one or more user input devices (e.g., user input device208) and one or more display devices (e.g., display device 210). In thismanner, a user may provide user input by way of the computing device tocontrol, program, configure, or otherwise interface with controller 104.The computing device may present information (e.g., output datagenerated by wearable sensor unit 102) by way of the one or more displaydevices.

FIG. 4 shows an alternative configuration 400 in which controller 104 isincluded within wearable sensor unit 102. Configuration 400 may allow auser of wearable sensor unit 102 to travel or otherwise move freelywhile still wearing wearable sensor unit 102 without having to ensurethat wearable sensor unit 102 is connected to a separate non-wearablecontroller.

In configuration 400, controller 104 may include one or more interfaces(e.g., wired or wireless interfaces) configured to facilitatecommunication between controller 104 and an external computing device.In this manner, a user may use the external computing device to control,program, configure, or otherwise interface with controller 104. Wearablesensor unit 102 may further include a power supply (not shown)configured to provide operating power to controller 104 and variousother components included in wearable sensor unit 102.

As another exemplary configuration, controller 104 may be included in awearable sensor unit other than wearable sensor unit 102. For example, amagnetic field measurement system may include a first wearable sensorunit and a second wearable sensor unit. A controller included in thefirst wearable sensor unit may be communicatively coupled to the secondwearable senor unit and configured to control both the first and secondwearable senor units. To this end, the first and second wearable sensorunits may be communicatively coupled by way of any suitablecommunication link.

As another exemplary configuration, controller 104 may be included in awearable device configured to be worn by a user and separate fromwearable sensor unit 102. For example, controller 104 may be included ina wearable device (e.g., a device that may be worn on the head, on theback (e.g., in a backpack), and/or on the waist (e.g., in a unitconfigured to clip or strap to a belt of the user)) and communicativelycoupled to wearable sensor unit 102 by way of any suitable communicationlink. Examples of this are described herein.

FIG. 5 shows an exemplary configuration 500 in which controller 104 isconfigured to concurrently interface with multiple wearable sensor units(e.g., multiple wearable sensor units configured to be worn concurrentlyby a user). For example, as shown, controller 104 is communicativelycoupled to wearable sensor unit 102-1 and wearable sensor unit 102-2(collectively “wearable sensor units 102”). As shown, both wearablesensor units 102 include a plurality of magnetometers 106 and a magneticfield generator 108. As shown, controller 104 may interface withmagnetometers 106 by way of communication links 110 and with magneticfield generators 108 by way of communication links 112.

As shown, the common clock signal output by clock source 202 isconfigured to be used by controller 104 to control or otherwiseinterface with all of the components of both wearable sensor units 102.In this manner, operation of and data output by wearable sensor units102 may be synchronized.

In the examples described above, controller 104 of system 100 maycontrol or interface with various components of one or more wearablesensor units 102 to measure biological or other magnetic fields. Asexplained above, a wearable sensor unit 102 may include, in someexamples, one or more magnetometers 106 and a magnetic field generator108. These components will now be described.

Magnetometers 106 may be any suitable magnetometers, such as but notlimited to optically pumped magnetometers (OPMs), nitrogen vacancy (NV)diamond sensors, and magnetoresistance sensors. OPMs may operate in avector mode and/or a scalar mode. In some examples, vector mode OPMs mayoperate at zero-fields and may utilize a spin exchange relaxation free(SERF) mode to reach femto-Tesla sensitivities.

FIG. 6 illustrates a block diagram of an exemplary magnetometer 106. Asshown, magnetometer 106 is an OPM. Magnetometer 106 includes a lightsource 602, a vapor cell 604, a signal photodetector 606, and a heater608. In addition, magnetic field generator 108 can be positioned aroundvapor cell 604. Magnetometer 106 may include additional or alternativecomponents as may suit a particular implementation, such as optics(e.g., lenses, waveplates, collimators, polarizers, and/or objects withreflective surfaces for beam shaping and polarization control and fordirecting light from light source 602 to vapor cell 604 and to signalphotodetector 606) and/or any other suitable components.

Light source 602 is configured to generate and emit light (e.g., laserlight) to optically pump alkali metal atoms in vapor cell 604 and toprobe vapor cell 604. Examples of suitable light source devices include,but are not limited to, a diode laser (e.g., a vertical-cavitysurface-emitting laser (VCSEL), a distributed Bragg reflector laser(DBR), a distributed feedback laser (DFB), etc.), a light-emitting diode(LED), a lamp, or any other suitable light source.

Vapor cell 604 contains an alkali metal vapor (e.g., rubidium in naturalabundance, isotopically enriched rubidium, potassium, or cesium, or anyother suitable alkali metal such as lithium, sodium, potassium,rubidium, cesium, or francium) and, optionally, a quenching gas (e.g.,nitrogen) and/or a buffer gas (e.g., nitrogen, helium, neon, or argon).It will be recognized that vapor cell 604 can contain additional orother gases or vapors as may suit a particular implementation. Heater608 is configured to heat vapor cell 604.

Signal photodetector 606 is configured to detect and measure opticalproperties (e.g., amplitude, phase, and/or polarization) of lightemitted by light source 602 that has passed through vapor cell 604.Examples of suitable signal photodetectors include, but are not limitedto, a photodiode, a charge coupled device (CCD) array, a CMOS array, acamera, a photodiode array, a single photon avalanche diode (SPAD)array, an avalanche photodiode (APD) array, and/or any other suitableoptical sensor array that can measure a change in transmitted light atthe optical wavelengths of interest.

Operation of magnetometer 106 will now be described. Light emitted bylight source 602 enters vapor cell 604 where it induces a transparentsteady state in the alkali metal vapor. In the transparent steady statethe light is allowed to pass through the vapor cell 604 with minimalabsorption by the alkali metal vapor and, hence, maximal detection bysignal photodetector 606. Magnetic fields generated from a target source(e.g., magnetic fields generated by a user's brain) cause thetransparency of the alkali metal vapor to decrease so that less light isdetected at signal photodetector 606. The change in light detected atsignal photodetector 606 is correlated to magnetic fields generated bythe target source.

However, ambient background magnetic fields may interfere with themeasurement by magnetometer 106 of magnetic fields generated by a targetsource. As used herein, the term “ambient background magnetic fields”refers to a magnetic field or magnetic fields associated with (e.g.,generated by) sources other than system 100 and the sources of interest(e.g., magnetic fields associated with neural signals from a user'sbrain). The ambient background magnetic fields can include, for example,the Earth's magnetic field as well as magnetic fields from magnets,electromagnets, electrical devices, and other signal or field generatorsin the environment other than magnetic field generator 108 that is partof system 100.

FIG. 7 shows the magnetic spectrum from 1 fT to 100 μT in magnetic fieldstrength on a logarithmic scale. The magnitude of magnetic fieldsgenerated by the human brain are indicated by range 702 and themagnitude of ambient background magnetic fields, including the Earth'smagnetic field, by range 704. The strength of the Earth's magnetic fieldcovers a range as it depends on the position on the Earth as well as thematerials of the surrounding environment where the magnetic field ismeasured. Range 706 indicates the approximate measurement range of amagnetometer (e.g., an OPM) operating in the SERF mode (e.g., a SERFmagnetometer) and range 708 indicates the approximate measurement rangeof a magnetometer operating in the scalar mode (e.g., a scalarmagnetometer.) Typically, a SERF magnetometer is more sensitive than ascalar magnetometer, but many conventional SERF magnetometers typicallyonly operate up to about 0 to 200 nT while the scalar magnetometerstarts in the 10 to 100 fT range but extends above 10 to 100 μT. At veryhigh magnetic fields the scalar magnetometer typically becomes nonlineardue to a nonlinear Zeeman splitting of atomic energy levels.

As can be seen from FIG. 7, SERF magnetometers have high sensitivitybut, conventionally, cannot function in a magnetic field higher thanabout 50 nT, which is approximately 1/1000 of the magnetic fieldstrength generated by the Earth. For a SERF magnetometer to accuratelymeasure biological and other weak signals, the strength of ambientbackground magnetic fields, including the Earth's magnetic field, needto be canceled or reduced to at least less than about 10-20 nT.Accordingly, wearable sensor unit 102 includes one or more activemagnetic field shields (e.g., magnetic field generator 108) and,optionally, one or more passive magnetic field shields. An activemagnetic field shield generates, for example, an equal and oppositemagnetic vector that cancels out, or substantially reduces, the ambientbackground magnetic fields. A passive magnetic field shield redirectsmagnetic fields away from magnetic field sensors (e.g., away frommagnetometers 106). Exemplary passive magnetic field shields aredescribed in more detail in U.S. patent application Ser. No. 16/457,655,which is incorporated herein by reference in its entirety.

Magnetic field generator 108 is configured to generate a compensationmagnetic field configured to actively shield a magnetic field sensingregion from ambient background magnetic fields. An ambient backgroundmagnetic field B is a vector magnetic field that has magnitude anddirection at each point in space. Using the Cartesian coordinate system,ambient background magnetic field B can be expressed as:

B=i·Bx+j·By+k·Bz

where Bx, By and Bz are the Cartesian components of the ambientbackground magnetic field and i, j, and k are unit vectors along the x-,y-, and z-axes. The compensation magnetic field B′ generated by magneticfield generator 108 is expressed as:

B′=i·Bx′+j·By′+k·Bz′

where Bx′, By′ and Bz′ are the Cartesian components of the compensationmagnetic field and i, j, and k are unit vectors along the x-, y-, andz-axes. In some examples, controller 104 may determine the compensationmagnetic field to be generated by magnetic field generator 108. Forexample, controller 104 may interface with one or more magnetic fieldsensors included in wearable sensor unit 102 to measure the ambientbackground magnetic field B. Controller 104 may determine thecompensation magnetic field B′ (e.g., determine the Bx′ component, theBy′ component, and/or the Bz′ component of compensation magnetic fieldB′) based on the measured ambient background magnetic field B. Exemplarymethods for determining a compensation magnetic field are described indetail in U.S. patent application Ser. No. 16/213,980, which isincorporated by reference herein in its entirety. Controller 104 maythen drive magnetic field generator 108 to generate the compensationmagnetic field.

The compensation magnetic field generated by magnetic field generator108 may actively shield the magnetic field sensing region by cancelingor substantially reducing (e.g., by at least 80%, 85%, 90%, 95%, or 99%,etc.) ambient background magnetic fields in one, two, or threedimensions. For example, magnetic field generator 108 may include one ormore of a Bz′ component generator, a Bx′ component generator, and/or aBy′ component generator configured to cancel or substantially reduceambient background magnetic fields along a z-axis, an x-axis, and/or ay-axis associated with magnetic field generator 108.

FIG. 8A illustrates an exemplary Bz′ component generator 800 of magneticfield generator 108. As shown, Bz′ component generator 800 includes aplurality of conductive windings 802 arranged in opposing parallelplanes. For example, Bz′ component generator 800 includes a firstconductive winding 802-1 arranged in a first plane and a secondconductive winding 802-2 arranged in a second plane that issubstantially parallel to the first plane. A magnetic field sensingregion 804 is located between conductive winding 802-1 and conductivewinding 802-2. Magnetic field sensing region 804 is a region where oneor more magnetometers 106 (e.g., vapor cells 604) may be located.

Bz′ component generator 800 is configured to actively shield magneticfield sensing region 804 (and hence magnetometers 106) from ambientbackground magnetic fields along a z-axis, such as by substantiallyreducing or canceling a Bz component of ambient background magneticfields at magnetic field sensing region 804. Legend 806 indicates anorientation of x-, y-, and z-axes, which have been arbitrarily assignedrelative to components of magnetic field generator 108. As indicated bylegend 806, the z-axis is a direction normal to the first plane and thesecond plane, the x-axis is a direction orthogonal to the z-axis andparallel to the first plane and the second plane, and the y-axis is adirection orthogonal to the z-axis and the x-axis and parallel to thefirst plane and the second plane.

Each conductive winding 802 comprises one or more coils, half coils,loops, and/or turns of conductive wiring forming a continuous electricalpath arranged substantially in a single plane. Conductive windings 802may be formed of any suitable conductor of electrical current, such asmetallic conductors (e.g., copper, silver, and/or gold) and non-metallicconductors (e.g., carbon). Each conductive winding 802 may be arrangedin a plane in any suitable way. In some examples, each conductivewinding 802 is arranged (e.g., etched, printed, soldered, deposited, orotherwise attached) on a planar substrate. The planar substrate may beformed of any suitable material, such as but not limited to alumina,ceramics, glass, and/or PCB material. FIG. 8B illustrates an exemplaryconfiguration of Bz′ component generator 800 in which conductive winding802-1 is arranged on an upper surface of a first PCB 808-1 andconductive winding 802-2 (not shown) is arranged on a bottom surface ofa second PCB 808-2. Second PCB 808-2 is substantially parallel to firstPCB 808-1. While PCBs 808 are shown to be round, they may be any othershape as may suit a particular implementation. PCBs 808 may be supportedand maintained in substantially parallel alignment in any suitable way,such as by one or more posts, screws, or other suitable supportingstructures.

FIGS. 9A-9D show exemplary functional diagrams of Bz′ componentgenerator 800 and illustrate various configurations in which conductivewindings 802 may be arranged on parallel planes. In FIGS. 9A-9Dconductive windings 802 are shown to have a vertical (z-direction)dimension above substrates 902 on which they are arranged. However, thisis only for illustration purposes, as conductive windings 802 may beimplemented by traces on substrates 902 or otherwise be embedded withinsubstrates 902.

FIG. 9A illustrates an exemplary configuration in which Bz′ componentgenerator 800 includes a single substrate 902. Conductive winding 802-1is arranged on a first surface 904-1 of substrate 902 and conductivewinding 802-2 is arranged on a second surface 904-2 of substrate 902.First surface 904-1 corresponds to the first plane and second surface904-2 corresponds to the second plane. Substrate 902 has a hole 906aligned with center openings of conductive windings 802. Magnetic fieldsensing region 804 is located in hole 906.

FIG. 9B illustrates another exemplary configuration in which Bz′component generator 800 includes two substrates 902 (e.g., firstsubstrate 902-1 and second substrate 902-2). Conductive winding 802-1 isarranged on an outer surface 904-1 of first substrate 902-1 (e.g., asurface facing away from magnetic field sensing region 804) andconductive winding 802-2 is arranged on an outer surface 904-2 of secondsubstrate 902-2 (e.g., a surface facing away from magnetic field sensingregion 804). Outer surface 904-1 corresponds to the first plane andouter surface 904-2 corresponds to the second plane.

FIG. 9C illustrates another exemplary configuration of Bz′ componentgenerator 800. FIG. 9C is the same as FIG. 9B except that conductivewinding 802-1 is arranged on an inner surface 904-3 of first substrate902-1 (e.g., a surface facing magnetic field sensing region 804) andconductive winding 802-2 is arranged on an inner surface 904-4 of secondsubstrate 902-2 (e.g., a surface facing magnetic field sensing region804). Inner surface 904-3 corresponds to the first plane and innersurface 904-4 corresponds to the second plane.

FIG. 9D illustrates another exemplary configuration of Bz′ componentgenerator 800. FIG. 9D is the same as FIG. 9B except that conductivewinding 802-1 is arranged on inner surface 904-3 of first substrate902-1 (e.g., a surface facing magnetic field sensing region 804), whileconductive winding 802-2 is arranged on outer surface 904-2 of secondsubstrate 902-2 (e.g., a surface facing away from magnetic field sensingregion 804). Inner surface 904-3 corresponds to the first plane andouter surface 904-2 corresponds to the second plane.

In the foregoing examples, Bz′ component generator 800 has twoconductive windings. However, Bz′ component generator 800 may have anyother number of conductive windings as may suit a particularimplementation, as illustrated in FIG. 10. FIG. 10 is the same as FIG.8A except that the plurality of conductive windings 802 further includesa conductive winding 802-3 arranged in a third plane and a conductivewinding 802-4 arranged in a fourth plane. The third plane and the fourthplane are substantially parallel to the first plane and the secondplane. Magnetic field sensing region 804 is located between conductivewindings 802-3 and 802-4. However, magnetic field sensing region 804 maybe located in any other suitable location.

Conductive windings 802-3 and 802-4 may be arranged on the third planeand the fourth plane in any manner described herein. FIG. 11A shows afunctional diagram of another exemplary configuration of Bz′ componentgenerator 800. FIG. 11A is the same as FIG. 9B except that conductivewinding 802-3 is arranged on inner surface 904-3 of first substrate902-1 and conductive winding 802-4 is arranged on inner surface 904-4 ofsecond substrate 902-2. Inner surface 904-3 corresponds to the thirdplane and inner surface 904-4 corresponds to the fourth plane. FIG. 11Billustrates an exemplary configuration of Bz′ component generator 800shown in FIGS. 10 and 11A. FIG. 11B is the same as FIG. 8B except thatconductive winding 802-3 (not visible in FIG. 11B) is arranged on aninner surface of first PCB 808-1 (e.g., a surface facing magnetic fieldsensing region 804) and conductive winding 802-4 is arranged on an innersurface of second PCB 808-2 (e.g., a surface facing magnetic fieldsensing region 804).

The foregoing examples show conductive windings 802-1 through 802-4arranged on two substrates (e.g., PCBs 808 or substrates 902). In otherexamples conductive windings 802-1 through 802-4 may be arranged on morethan two substrates. For instance, each conductive winding 802 may eachbe arranged on a separate substrate. However, arranging multipleconductive windings 802 on a single substrate (e.g., on oppositesurfaces of a substrate, as illustrated in FIGS. 11A and 11B) fixes thealignment of the conductive windings 802 relative to one another andthus prevents inadvertent misalignments.

In the examples described above, conductive windings 802 may have anywinding pattern as may suit a particular implementation. As used herein,a winding pattern may refer to the path of conductive wiring, thespacing between adjacent wires, a width/thickness of wires, the numberof loops or turns, the direction of current flow, and the like. In someexamples the winding patterns of conductive windings 802 may beautomatically generated by a magnetic field generator design systemconfigured to optimize the winding patterns based on a set of inputs. Anexemplary magnetic field generator design system will be described belowin more detail. Generally, the winding patterns of conductive windings802 are configured to generate a homogeneous magnetic field at themagnetic field sensing region. The winding patterns may be configured togenerate a homogeneous magnetic field that is approximately 30% the sizeof conductive windings 802, as measured along the x- or y-direction.

In some examples, winding patterns of the plurality of conductivewindings are substantially identical (e.g., mirror images of oneanother). For example, conductive winding 802-1 may be substantiallyidentical to conductive winding 802-2. Additionally, conductive windings802-3 and 802-4 may be substantially identical to each other and/or toconductive windings 802-1 and 802-2.

In some examples, conductive windings 802 may grouped into pairs (e.g.,based on a drive current supplied, a location of conductive windings802, etc.) such that conductive windings 802 within a particular pairhave the same winding patterns, but different pairs of conductivewindings 802 have different winding patterns. For instance, windingpatterns of conductive windings 802-1 and 802-2 may be substantiallyidentical, and winding patterns of conductive windings 802-3 and 802-4may be substantially identical but different from the winding patternsof conductive windings 802-1 and 802-2.

In some examples, conductive windings 802 within a particular pair ofconductive windings have different winding patterns. For instance,winding patterns of conductive windings 802-1 and 802-2 may be differentfrom one another. This may be desirable when magnetic sensing region 804is off-center in the z-direction (e.g., is closer to first substrate902-1 or second substrate 902-2). Winding patterns of conductivewindings 802-3 and 802-4 may be substantially identical or may also bedifferent from one another.

Controller 104 is configured is to drive conductive windings 802 bysupplying one or more drive currents to conductive windings 802. FIG. 12shows an exemplary functional diagram indicating how controller 104 maydrive Bz′ component generator 800. As shown, controller 104 may supply afirst drive current 1202-1 to conductive winding 802-1 and supply asecond drive current 1202-2 to conductive winding 802-2. Drive currents1302 may be supplied, for example, by way of communication link 112.

FIG. 13 illustrates another exemplary schematic illustrating howcontroller 104 may drive Bz′ component generator 800. FIG. 13 is thesame as FIG. 12 except that Bz′ component generator 800 further includesconductive windings 802-3 and 802-4. Accordingly, controller 104 isconfigured to supply a third drive current 1202-3 to conductive winding802-3 and supply a fourth drive current 1202-4 to conductive winding802-4. Drive currents 1202-3 and 1202-4 may be supplied by way ofcommunication link 112.

Conductive windings 802 are configured to generate a Bz′ component of acompensation magnetic field when conductive windings 802 are suppliedwith drive currents 1202. The Bz′ component of the compensation magneticfield is configured to actively shield magnetic field sensing region 804from ambient background magnetic fields along the z-axis, such as byreducing or canceling a Bz component of ambient background magneticfields. In some examples, the Bz′ component of the compensation magneticfield is substantially equal and opposite to the Bz component of theambient background magnetic fields.

Controller 104 may drive conductive windings 802 in any suitable way.For example, controller 104 may supply conductive windings 802 with thesame drive current 1202. In other words, drive currents 1202 may all bethe same current. In some examples controller 104 includes a singledriver configured to supply all drive currents 1202 to conductivewindings 802. In alternative examples, controller 104 includes aplurality of individual drivers each configured to supply a drivecurrent 1202, but controller 104 controls the drivers to supply the samedrive current to conductive windings 802. By driving conductive windings802 such that drive currents 1202 are the same, conductive windings 802generate a uniform magnetic field along the z-direction in magneticfield sensing region 804.

Alternatively to supplying conductive windings 802 with the same drivecurrent, controller 104 may supply one or more of conductive windings802 with a drive current that is different from drive currents suppliedto other conductive windings 802. For example, drive current 1202-1 maybe different from drive current 1202-2. Additionally or alternatively,drive current 1202-3 may be different from drive current 1202-4. Whenconductive windings 802-1 and 802-2 are driven with different drivecurrents, Bz′ component generator 800 generates a gradient magneticfield (e.g., a dBz′/dz gradient). When conductive windings 802-1 and802-2 are driven with different drive currents and conductive windings802-3 and 802-4 are driven with the same drive (or vice versa), Bz′component generator 800 generates a gradient magnetic field in additionto the Bz′ component of the compensation magnetic field. The gradientmagnetic field is configured to actively shield magnetic field sensingregion from fields that linearly vary along the z-axis, as will beexplained below in more detail.

As mentioned above, magnetic field generator 108 may include, inaddition to or in place of Bz′ component generator 800, a Bx′ componentgenerator and/or a By′ component generator configured to cancel orsubstantially reduce ambient background magnetic fields along the x-axisand/or the y-axis.

FIGS. 14A-14C illustrate an exemplary configuration of a Bx′/By′component generator 1400 of magnetic field generator 108. FIGS. 14A and14B show plan views (e.g., views in the z-direction) of Bx′/By′component generator 1400, and FIG. 14C is a side view functional diagramof Bx′/By′ component generator 1400 (e.g., as viewed in the y-direction)taken along the dashed lines labeled XIV-XIV. Legend 1402 indicates anorientation of x-, y-, and z-axes. The orientation of legend 1402 is thesame as the orientation of legend 806 relative to magnetic fieldgenerator 108.

As shown, Bx′/By′ component generator 1400 includes a first substrate1404-1 and a second substrate 1404-2 positioned opposite to firstsubstrate 1404-1 and separated from first substrate 1404-1 in thez-direction by a gap. Substrates 1404 may be formed of any suitablematerial, such as but not limited to alumina, ceramics, glass, and/orPCB board. In some examples in which magnetic field generator 108includes Bx′/By′ component generator 1400 in addition to Bz′ componentgenerator 800, substrates 1404 and substrates 902 are the same (e.g.,substrate 1404-1 is implemented by substrate 902-1 and substrate 1404-2is implemented by substrate 902-2). In alternative examples, substrates1404 are different than substrates 902. Exemplary configurations ofmagnetic field generator 108 will be described below in more detail.Substrates 1404 are shown to have an octagonal shape. However,substrates 1404 may have any shape as may suit a particularimplementation.

A magnetic field sensing region 1406 is located in the gap (see FIG.14C). Magnetic field sensing region 1406 is a region where one or moremagnetometers 106 (including respective vapor cells 604) may be located.In some examples in which Bx′/By′ component generator 1400 is used incombination with Bz′ component generator 800, magnetic field sensingregion 1406 is the same as magnetic field sensing region 804.

A first wiring set 1408-1 is arranged on first substrate 1404-1 and asecond wiring set 1408-2 is arranged on second substrate 1404-2. Eachwiring set 1408 comprises a plurality of electrically unconnected wiresextending generally along the y-direction. Wiring sets 1408 may beformed of any suitable conductor of electrical current, such as metallicconductors (e.g., copper, silver, and/or gold) and non-metallicconductors (e.g., carbon). Wiring sets 1408 may be arranged onsubstrates 1404 in any suitable manner (e.g., etched, printed, soldered,deposited, or otherwise attached).

Interconnects 1410 (e.g., first interconnect 1410-1 and secondinterconnect 1410-2) are positioned between first substrate 1404-1 andsecond substrate 1404-2. Interconnects 1410 electrically connect firstwiring set 1408-1 with second wiring set 1408-2 to thereby form acontinuous electrical path (as represented by the dashed line in FIG.14C) through first wiring set 1408-1 and second wiring set 1408-2.Interconnects 1410 may electrically connect to wiring sets 1408 in byconnections 1414 (e.g., one or more relays, contact pads, wires, etc.).Interconnects 1410 may comprise any suitable electrical connectorconfigured to electrically connect first wiring set 1408-1 on firstsubstrate 1404-1 with second wiring set 1408-2 on second substrate1404-2. In some examples, each interconnect 1410 is an elastomericconnector that is anisotropically conductive in the z-direction.Suitable elastomeric connectors may include, for example, zebraconnectors commercially available from Fujipoly America Corp.

FIGS. 15A and 15B illustrate exemplary configurations of an elastomericconnector that may be used as interconnects 1410. As shown in FIG. 15A,a lamination-type elastomeric connector 1500A includes a plurality ofthin, planar conductive elements 1502, each of which is electricallyisolated from other conductive elements 1502 by intervening isolationelements 1504. Conductive elements 1502 may be formed of any suitableconductive material (e.g., silver, gold, copper, etc.). Isolationelements 1504 may be formed of any suitable electrically insulatingmaterial (e.g., an elastomeric material). Conductive elements 1502 andisolation elements 1504 are stacked in an alternating pattern. In someexamples, as shown in FIG. 15A, conductive elements 1502 and isolationelements 1504 are enclosed between side support barriers 1506-1 and1506-2. Side support barriers 1506 may also be formed of a suitableelectrically insulating material. When elastomeric connector 1500A ispositioned between substrates 1404, each conductive element 1502 isoriented in the z-direction and makes contact with first substrate1404-1 and second substrate 1404-2 (e.g., with contact pads on firstsubstrate 1404-1 and second substrate 1404-2).

FIG. 15B illustrates an exemplary matrix-type elastomeric connector1500B. Elastomeric connector 1500B is the same as elastomeric connector1500A except that conductive elements 1502 comprise fine conductivewires embedded within an elastomer matrix 1508.

Referring again to FIGS. 14A-14C, continuous electrical path 1412 formsa conductive winding configured to generate, when supplied with a drivecurrent, a Bx′ component of a compensation magnetic field. The Bx′component of the compensation magnetic field is configured to activelyshield magnetic field sensing region 1406 from ambient backgroundmagnetic fields along the x-axis. For example, Bx′/By′ componentgenerator 1400 may substantially reduce or cancel a Bx component ofambient background magnetic fields at magnetic field sensing region1406. In some examples, the Bx′ component of the compensation magneticfield is substantially equal and opposite to the Bx component of theambient background magnetic fields.

In alternative embodiments, Bx′/By′ component generator 1400 may beconfigured to generate a By′ component of the compensation magneticfield. FIGS. 16A-16C illustrate another exemplary configuration ofBx′/By′ component generator 1400. FIGS. 16A-16C are the same as FIGS.14A-14C except that wiring sets 1408 extend generally in thex-direction. Thus, continuous electrical path 1412 forms a conductivewinding configured to generate, when supplied with a drive current, aBy′ component of a compensation magnetic field. The By′ component of thecompensation magnetic field is configured to actively shield magneticfield sensing region 1406 from ambient background magnetic fields alongthe y-axis. For example, Bx′/By′ component generator 1400 maysubstantially reduce or cancel a By component of ambient backgroundmagnetic fields at magnetic field sensing region 1406. In some examples,the By′ component of the compensation magnetic field is substantiallyequal and opposite to the By component of the ambient backgroundmagnetic fields.

In some embodiments, Bx′/By′ component generator 1400 is configured toactively shield magnetic field sensing region 1406 from ambientbackground magnetic fields in both the x-direction and the y-direction.FIGS. 17A-17C show another exemplary configuration of Bx′/By′ componentgenerator 1400. FIGS. 17A-17C are the same as FIGS. 14A-14C except thata third wiring set 1408-3 is arranged on first substrate 1404-1 inaddition to first wiring set 1408-1, and a fourth wiring set 1408-4 isarranged on second substrate 1404-2 in addition to second wiring set1408-2. First wiring set 1408-1 and second wiring set 1408-2 extendgenerally in the y-direction while third wiring set 1408-3 and fourthwiring set 1408-4 extend generally in the x-direction. Interconnects1410-1 and 1410-2 electrically connect first wiring set 1408-1 withsecond wiring set 1408-2 to form a first continuous electrical path 1412through first wiring set 1408-1 and second wiring set 1408-2, andinterconnects 1410-3 and 1410-4 electrically connect third wiring set1408-3 with fourth wiring set 1408-4 to thereby form a second continuouselectrical path (not shown in FIG. 17C) through third wiring set 1408-3and fourth wiring set 1408-4. Interconnects 1410-3 and 1410-4 may beimplemented, for example, by an elastomeric connector, as describedabove. As shown in FIGS. 17A and 17B, interconnects 1410 are formed by asingle elastomeric connector that surrounds magnetic field sensingregion 1406. In other embodiments, interconnects 1410 are not connectedto one another but are separate structures.

As shown in FIG. 17C, first continuous electrical path 1412 forms afirst conductive winding configured to generate, when supplied with adrive current, a Bx′ component of a compensation magnetic field. Thesecond continuous electrical path (not shown) forms a second conductivewinding configured to generate, when supplied with a drive current, aBy′ component of the compensation magnetic field.

As shown in FIG. 17C, first wiring set 1408-1 and third wiring set1408-3 are both arranged on first substrate 1404-1, and second wiringset 1408-2 and fourth wiring set 1408-4 are both arranged on secondsubstrate 1404-2. In this embodiment, first wiring set 1408-1 isseparated from third wiring set 1408-3 by an electrical insulator (notshown) and second wiring set 1408-2 is separated from fourth wiring set1408-4 by an electrical insulator (not shown). In alternativeembodiments, first wiring set 1408-1 and third wiring set 1408-3 arearranged on opposite surface of first substrate 1404-1, and secondwiring set 1408-2 and fourth wiring set 1408-4 are arranged on oppositesurface of second substrate 1404-2. In yet other embodiments, eachwiring set 1408 is arranged on a different substrate.

In the examples described above, wiring sets 1408 (and hence conductivewindings formed by wiring sets 1408) may have any winding pattern as maysuit a particular implementation. In some examples the winding patternsof wiring sets 1408 may be automatically generated by a magnetic fieldgenerator design system configured to optimize the winding patternsbased on a set of inputs. An exemplary magnetic field generator designsystem will be described below in more detail. Generally, the windingpatterns of the Bx′ component and/or By′ component conductive windingsare configured to generate a homogeneous magnetic field at the magneticfield sensing region. The winding patterns may be configured to generatea homogeneous magnetic field that is approximately 30% the size ofwiring sets 1408, as measured along the x- or y-direction.

As mentioned above, in some embodiments magnetic field generator 108includes both Bz′ component generator 800 and Bx′/By′ componentgenerator 1400. With this configuration magnetic field generator 108 isconfigured to actively shield magnetic field sensing region 804/1406from ambient background magnetic fields along the x-, y-, and z-axes. Insome examples, conductive windings 802 of Bz′ component generator 800are arranged on substrates 1404 of Bx′/By′ component generator 1400. Insuch examples conductive windings 802 are electrically insulated fromwiring sets 1408. In alternative examples, conductive windings 802 ofBz′ component generator 800 are arranged on substrates (e.g., substrates902 of Bz′ component generator 800) that are different from substrates1404 of Bx′/By′ component generator 1400. An exemplary physicalimplementation of magnetic field generator 108 will be described belowin more detail.

As mentioned, magnetic field generator 108 is configured to activelyshield a magnetic sensing region from ambient magnetic fields along thex-, y, and/or z-axes. In some examples, magnetic field generator 108 isfurther configured to actively shield the magnetic sensing region fromfirst-order gradient magnetic fields, e.g., ambient background magneticfields that linearly vary in the x-, y-, and/or z-direction. The ambientbackground magnetic field B is a vector magnetic field that hasmagnitude and direction at each point in space. Using the Cartesiancoordinate system, ambient background magnetic field B can be expressedas:

B=i·Bx+j·By+k·Bz

where Bx, By and Bz are the Cartesian components of the ambientbackground magnetic field and i, j, and k are unit vectors along the x-,y-, and z-axes. The gradient of B, denoted VB, is a second order tensor,a matrix of nine partial derivatives of the three principal componentsof B (Bx, By, and Bz) with respect to the three cardinal axes (x, y, andz):

${\nabla B} = \begin{bmatrix}\frac{dBx}{dx} & \frac{dBy}{dx} & \frac{dBz}{dx} \\\frac{dBx}{dy} & \frac{dBy}{dy} & \frac{dBz}{dy} \\\frac{dBx}{dz} & \frac{dBy}{dz} & \frac{dBz}{dz}\end{bmatrix}$

As can be seen from ∇B, there are nine possible gradient components ofthe ambient background magnetic fields. Accordingly, magnetic fieldgenerator 108 may further be configured to actively shield magneticfield sensing regions 804 and/or 1406 from any one or more of thegradient components of the ambient background magnetic fields. However,in some examples it is not necessary to generate every gradientcomponent of the compensation magnetic field. Instead, the gradientscomponents of the ambient background magnetic fields can be activelyshielded by generating a subset of gradient components of thecompensation magnetic field, as will now be described.

As mentioned above, Bz′ component generator 800 is configured togenerate one or more z-axis gradient components of the compensationmagnetic field when at least two conductive windings 802 (e.g.,conductive windings 802-1 and 802-2) are driven with different drivecurrents. For example, controller 104 may be configured to drive Bz′component generator 800 to generate a dBz′/dz gradient component, adBz′/dx gradient component, and/or a dBz′/dy gradient component of thecompensation magnetic field.

In some embodiments, Bx′/By′ component generator 1400 may also beconfigured to generate one or more gradient components of thecompensation magnetic field. FIGS. 18A-18C illustrate an exemplaryconfiguration of Bx′/By′ component generator 1400 having conductivewindings configured to generate gradient components of the compensationmagnetic field. FIGS. 18A and 18B show plan views (e.g., views in thez-direction) of Bx′/By′ component generator 1400, and FIG. 18C is aperspective view of various conductive windings included in Bx′/By′component generator 1400. Legend 1402 indicates an orientation of x-,y-, and z-axes. In FIGS. 18A-18C, wiring sets 1408 have been omitted tofacilitate discussion of the gradient component conductive windings.

As shown in FIG. 18A, first substrate 1404-1 includes a first gradientwiring 1802-1 extending generally in the y-direction along a first edgeof first substrate 1404-1 and a second gradient wiring 1802-2 extendinggenerally in the y-direction along a second edge of first substrate1404-1. First gradient wiring 1802-1 and second gradient wiring 1802-2are substantially parallel to each other and are represented by dashedlines. First substrate 1404-1 also includes a third gradient wiring1802-3 extending generally in the x-direction along a third edge offirst substrate 1404-1 and a fourth gradient wiring 1802-4 extendinggenerally in the x-direction along a fourth edge of first substrate1404-4. Third gradient wiring 1802-3 and fourth gradient wiring 1802-4are substantially parallel to each other and are represented bydash-dot-dash lines. Third gradient wiring 1802-3 and fourth gradientwiring 1802-4 are not electrically connected to first gradient wiring1802-1 or second gradient wiring 1802-1.

As shown in FIG. 18B, second substrate 1404-2 includes a fifth gradientwiring 1802-5 extending generally in the y-direction along a first edgeof second substrate 1404-2 and a sixth gradient wiring 1802-6 extendinggenerally in the y-direction along a second edge of second substrate1404-2. Fifth gradient wiring 1802-5 and sixth gradient wiring 1802-6are substantially parallel to each other and are represented by dashedlines. Second substrate 1404-2 also includes a seventh gradient wiring1802-7 extending generally in the x-direction along a third edge ofsecond substrate 1404-2 and an eighth gradient wiring 1802-8 extendinggenerally in the x-direction along a fourth edge of second substrate1404-2. Seventh gradient wiring 1802-7 and eighth gradient wiring 1802-8are substantially parallel to each other and are represented bydash-dot-dash lines. Seventh gradient wiring 1802-7 and eighth gradientwiring 1802-8 are not electrically connected to fifth gradient wiring1802-5 or sixth gradient wiring 1802-6.

Gradient wirings 1802 may each comprise one or more wires and may beformed of any suitable conductor of electrical current, such as metallicconductors (e.g., copper, silver, and/or gold) and non-metallicconductors (e.g., carbon). Gradient wirings 1802 may be arranged onsubstrates 1404 in any suitable manner (e.g., etched, printed, soldered,deposited, or otherwise attached). Furthermore, gradient wirings 1802may be arranged on any surfaces of substrates 1404 as may suit aparticular implementation.

When interconnects 1410 are positioned between first substrate 1404-1and second substrate 1404-2, as shown in FIGS. 17A-17C, interconnects1410 electrically connect gradient wirings 1802 on first substrate1404-1 with gradient wirings 1802 on second substrate 1404-2. Forexample, interconnects 1410 electrically connect first gradient wiring1802-1 with fifth gradient wiring 1802-5 to thereby form a firstcontinuous electrical path, which forms a first conductive winding1804-1, as shown in FIG. 18C. Similarly, interconnects 1410 electricallyconnect second gradient wiring 1802-2 with sixth gradient wiring 1802-6to thereby form a second continuous electrical path, which forms asecond conductive winding 1804-2. Interconnects 1410 also electricallyconnect third gradient wiring 1802-3 with seventh gradient wiring 1802-7to thereby form a third continuous electrical path, which forms a thirdconductive winding 1804-3. Interconnects 1410 further electricallyconnect fourth gradient wiring 1802-4 with eighth gradient wiring 1802-8to thereby form a fourth continuous electrical path, which forms afourth conductive winding 1804-4.

To generate a dBx′/dx gradient component of the compensation magneticfield, controller 104 drives first conductive winding 1804-1 and secondconductive winding 1804-2 with equal but opposite currents. Thecombination of the magnetic fields generated by conductive windings1804-1 and 1804-2 generates a dBx′/dx gradient component that linearlyvaries in the x-direction. Similarly, to generate a dBy′/dy gradientcomponent of the compensation magnetic field, controller 104 drivesthird conductive winding 1804-3 and fourth conductive winding 1804-4with equal but opposite currents. The combination of the magnetic fieldsgenerated by conductive windings 1804-3 and 1804-4 generates a dBy′/dygradient component that linearly varies in the y-direction.

Bx′/By′ component generator 1400 is further configured to generate acombination gradient component that is the sum of dBx′/dy and dBy′/dxgradient components of the compensation magnetic field. To this end,first substrate 1404-1 further includes a fifth conductive winding1804-5 that is formed of four L-shaped loops 1806 (e.g., loops 1806-1 to1806-4) positioned at each corner of first substrate 1404-1. In someexamples, as shown in FIGS. 18A-18C, loops 1806 are connected to eachother in series. Second substrate 1404-2 includes a sixth conductivewinding 1804-6 that is formed of four L-shaped loops 1806 (e.g., loops1806-5 to 1806-8) positioned at each corner of second substrate 1404-2.In some examples, as shown in FIGS. 18A-18C, loops 1806 are connected toeach other in series. Conductive windings 1804-5 and 1804-6 are notelectrically connected to each other, whether by interconnects 1410 orotherwise. Controller 104 may drive conductive windings 1804-5 and1804-6 with equal but opposite drive currents to thereby generate acombination gradient component that is the sum of dBx′/dy and dBy′/dxgradient components.

It will be recognized that the configuration of conductive windings 1804described above is merely exemplary and not limiting, as conductivewindings 1804 may have any other configuration or winding pattern as maysuit a particular implementation. Furthermore, in alternativeembodiments Bx′/By′ component generator 1400 may not include allconductive windings 1804. For example, if Bx′/By′ component generator1400 is configured to actively shield magnetic field sensing region 1406from ambient background magnetic fields in only the x-direction, Bx′/By′component generator 1400 may include only conductive windings 1804-1 and1804-2.

As mentioned, magnetic field generator 108 can be used in wearablesensor unit 102 to actively shield one or more magnetometers 106included in wearable sensor unit from ambient background magneticfields. FIG. 19 shows a perspective view of an exemplary physicalimplementation 1900 of wearable sensor unit 102. As shown, physicalimplementation 1900 includes PCBs 1902-1 and 1902-2 (collectively “PCBs1902”) and substrates 1904-1 through 1904-4 (collectively “substrates1904”). In some examples, substrates 1904 may be implemented by PCBs.

PCBs 1902 and substrates 1904 are structurally arranged as shown. Inparticular, PCB 1902 is located at a “top” side of physicalimplementation 1900 (i.e., a side furthest away from a head or othersurface upon which wearable sensor unit 102 is placed to detect magneticfields) and substrate 1904-2 is located at a “bottom” side of physicalimplementation 1900 (i.e., a side closest to a head or other surfaceupon which wearable sensor unit 102 is placed to detect magneticfields).

Interconnect 1905 is disposed between substrates 1904-3 and 1904-5 andmaintains a spacing between substrates 1904-3 and 1904-5. A magneticfield sensing region (not shown in FIG. 19) is located betweensubstrates 1904-3 and 1904-5 and surrounded by interconnect 1905. Anarray of vapor cells (not shown) is located within the magnetic fieldsensing region.

Conductive windings that constitute magnetic field generator 108 aredisposed on substrates 1904. For example, conductive windings configuredto generate the Bz′ component of the compensation magnetic field may bedisposed on substrates 1904-1 and 1904-2. Conductive windings configuredto generate the Bx′ and By′ components of the compensation magneticfield include wiring sets disposed on substrates 1904-3 and 1904-4 andconductive elements in interconnect 1905. Conductive windings configuredto generate gradient components of the compensation magnetic field mayadditionally be disposed on substrates 1904-1 through 1904-4 and ininterconnect 1905.

PCB 1902-1 includes various components disposed thereon that areassociated with light sources included in each magnetometer 106. Forexample, PCB 1902-1 may include light sources (e.g., light source 602),heaters for the light sources, thermistors for the light sources, andmonitor photodetectors for the light sources disposed thereon. As shown,PCB 1902-1 may also include a plurality of twisted pair cable interfaceassemblies 1906 disposed thereon. In particular, twisted pair cableinterface assembly 1906-1 is electrically connected to inputs of thelight sources, twisted pair cable interface 1906-2 is electricallyconnected to inputs of the heaters, twisted pair cable interface 1906-3is electrically connected to outputs of the thermistors, and twistedpair cable interface 1906-4 is electrically connected to outputs of themonitor photodetectors.

PCB 1902-2 may include signal photodetectors (e.g., signal photodetector606) and a twisted pair cable interface 1906-5 electrically connected tooutputs of the signal photodetectors. A twisted pair cable interface1906-6 electrically connected to inputs of heaters (e.g., heater 608)for the signal photodetectors is disposed on a mount 1908 locatedproximate to PCB 1902-2.

As shown, coaxial cable interface assemblies 1910-1 through 1910-9(collectively “coaxial cable interface assemblies 1910”) are located onsubstrates 1904. Coaxial cable interface assemblies 1910 areconductively coupled to the conductive windings that constitute magneticfield generator 108. As described herein, controller 104 may drive theconductive windings by supplying drive current to the conductivewindings by way of coaxial cables connected to coaxial cable interfaceassemblies 1910.

Physical implementation 1900 may include any additional or alternativecomponents as may suit a particular implementation (e.g., a housing tohouse at least some of the components shown in FIG. 19, supportstructures to support substrates 1904, etc.).

FIG. 20 shows a cross-sectional side view of physical implementation1900 of wearable sensor unit 102 and illustrates various components ofmagnetometers 106 that are located within wearable sensor unit 102. Forexample, FIG. 20 shows that a plurality of light sources (e.g., lightsource 2002, which may implement any of the light sources describedherein), a plurality of thermistors (e.g., thermistor 2004), and aplurality of monitor photodetectors (e.g., monitor photodetector 2006)are disposed on an underneath side of PCB 1902-1.

Light generated by light sources is collimated by a plurality ofcollimating lenses (e.g., collimating lens 2008) and passes throughoptics (e.g., optics 2010). Optics may include, for example, a prism foreach magnetometer that is configured to reflect the light onto themonitor photodiodes. The light also passes through the optics, thenthrough holes (e.g., hole 2012) in substrate 1904-3, then throughchimneys (e.g., chimney 2014), and into vapor cells (e.g., vapor cell2016, which may implement any of the vapor cells described herein). Thechimneys are configured to prevent heat from the vapor cells from goingback up through the holes.

In the implementation of FIG. 20, the light from the light sourcespasses through the vapor cells, then through a second set of chimneys(e.g., chimney 2018), and then through holes (e.g., hole 2020) insubstrate 1904-4. The light is then detected by signal photodetectors(e.g., signal photodetector 2022, which may implement any of the signalphotodetectors described herein).

In some examples a wearable device that may be worn by a user mayinclude a plurality of wearable sensor units. FIG. 21A illustrates afunctional diagram of an exemplary wearable device 2100. Wearable device2100 is configured to be worn by a user (e.g., on a head of the user).For example, wearable device 2100 may be conformable to a shape of auser's head. In some examples, wearable device 2100 is portable. Inother words, wearable device 2100 may be small and light enough to beeasily carried by a user and/or worn by the user while the user movesaround and/or otherwise performs daily activities.

As shown, wearable device 2100 includes a plurality of wearable sensorunits 102 (e.g., wearable sensor units 102-1 through 102-3). However,wearable device 2100 may include any other suitable number of wearablesensor units 102. For example, wearable device 2100 may include an arrayof two, five, nine, twelve, twenty-five, or any other suitable pluralityof wearable sensor units 102 as may serve a particular implementation.Furthermore, wearable sensor units 102 may be positioned within wearabledevice 2100 in any arrangement as may suit a particular implementation.

As mentioned above, each wearable sensor unit 102 includes a pluralityof magnetometers 106 configured to detect a relatively weak magneticfield (e.g., magnetic fields that come from the brain), and a magneticfield generator 108 configured to actively shield magnetometers 106(e.g., vapor cells 604) from ambient background magnetic fields.Magnetic field generators 108 actively shield magnetometers 106 bygenerating a compensation magnetic field when supplied with a drivecurrent.

However, magnetic field generators 108 (e.g., conductive windings 802,Bx′/By′ component conductive windings, and/or conductive windings 1804of magnetic field generators 108) may also generate fringe magneticfields 2102 (e.g., fringe magnetic fields 2102-1 through 2102-3) thatextend beyond magnetic field generators 108, as illustrated in FIG. 21A.As a result, fringe magnetic fields 2102 may be detected bymagnetometers 106 of nearby wearable sensor units 102. For example,wearable sensor unit 102-1 generates a fringe magnetic field 2102-1 thatmay be detected by magnetometers 106 in wearable sensor units 102-2and/or 102-3. Thus, fringe magnetic field 2102-1 may interfere with thedetection, by wearable sensor units 102-2 and 102-3, of the magneticfields from the intended source (e.g., the user's brain). Additionally,magnetic field generators 108 of wearable sensor units 102 may attemptto compensate for detected fringe magnetic fields 2102 in addition tocompensating for ambient background magnetic fields. However, asmagnetic field generators 108 of multiple different wearable sensorunits 102 attempt to compensate for detected fringe magnetic fields 2102at the same time, wearable sensor units 102 (e.g., drive currentssupplied by controller 104) may begin to oscillate and prevent magneticfield generators 108 from reaching a steady-state. This may occur evenwhen the ambient background magnetic fields are relatively static.

To prevent such magnetic coupling between wearable sensor units 102,wearable device 2100 is configured such that the strength of the fringemagnetic fields 2102 at each wearable sensor unit 102 is less than apredetermined value (e.g., less than about 10 nT, less than about 20 nT,etc.) at a predetermined distance from the magnetic field generator(e.g., at a plurality of magnetometers). With this configuration,magnetic field generators 108 included in wearable sensor units 102 donot compensate, or need to compensate, for fringe magnetic fields 2102generated by neighboring wearable sensor units 102.

FIG. 21B illustrates an exemplary configuration of wearable device 2100that reduces or eliminates magnetic coupling. FIG. 21B is the same asFIG. 21A except that wearable sensor units 102 are spaced apart from oneanother such that the strength of fringe magnetic fields 2102 at eachwearable sensor unit 102 (e.g., at a magnetic field sensing region ofwearable sensor unit 102 and/or at one or more sensors included inwearable sensor unit 102) is less than a predetermined value (e.g., lessthan about 10 nT, less than about 20 nT, etc.) at a predetermineddistance from the magnetic field generator (e.g., from each conductivewinding). In some examples, the spacing between wearable sensor units102 is determined by a magnetic field generator design system, as willbe described below in more detail. The magnetic field generator designsystem may model the fringe magnetic fields 2102 to determine an optimalspacing.

FIG. 21C illustrates another example in which the spatial extent of eachfringe magnetic field 2102 is reduced. By reducing the spatial extent offringe magnetic fields 2102 at a predetermined distance from the sourceof the fringe magnetic field 2102, the strength of the fringe magneticfields 2102 at each wearable sensor unit 102 (e.g., at eachmagnetometer) may be reduced to less than a predetermined value (e.g.,less than about 10 nT, less than about 20 nT, etc.). The spatial extentof each fringe magnetic field 2102 may be reduced in any suitable way.In some examples each magnetic field generator 108 (e.g., Bz′ componentgenerator 800 and/or Bx′/By′ component generator 1400) includes one ormore counter-windings configured to reduce the extent of the fringemagnetic field generated by the conductive windings of magnetic fieldgenerator 108. For instance, a winding pattern of conductive windings802, Bx′/By′ component conductive windings, and/or conductive windings1804) may include a counter-winding at an outer portion of theconductive winding (e.g., at a portion of the conductive windingfarthest away from the magnetic field sensing region). In thecounter-winding, drive current flows opposite to the direction of thedrive current in the conductive winding. As a result, the spatial extentof the fringe field generated by the conductive winding is shortened(e.g., magnetic field lines from the conductive winding bend back towardthe conductive winding earlier than without the counter-winding). Insome examples, the winding pattern and configuration of thecounter-winding is determined by the magnetic field generator designsystem, as will be described below in more detail.

FIGS. 22-26 illustrate exemplary physical implementations of a wearabledevice 2200. Wearable device 2200 may implement wearable device 2100.Wearable device 2200 includes elements of the wearable sensor unitsdescribed herein. For example, wearable device 2200 includes a pluralityof magnetometers 2202 and a plurality of magnetic field generators 2203(shown in FIG. 22). The various exemplary physical implementations ofwearable device 2200 may each also include a controller (e.g.,controller 104) and/or be communicatively connected to a controller. Itwill be recognized that the physical implementations of wearable device2200 shown in FIGS. 22-27 are merely illustrative and not limiting. Ingeneral, wearable device 2200 may be implemented by any suitableheadgear and/or clothing article configured to be worn by a user. Theheadgear and/or clothing article may include batteries, cables, and/orother peripherals for the components of the wearable sensor unitsdescribed herein.

FIG. 22 illustrates an embodiment of a wearable device 2200 in the formof a helmet with a handle 2204. A cable 2206 extends from the wearabledevice 2200 for attachment to a battery or hub (with components such asa controller, processor, or the like). FIG. 23 illustrates anotherembodiment of a wearable device 2200 in the form of a helmet showing aback view. FIG. 24 illustrates a third embodiment of a wearable device2200 in the form of a helmet with cable 2206 leading to a wearablegarment 2208 (such as a vest or partial vest) that can include a batteryor a hub. Alternatively or additionally, the wearable device 2200 caninclude a crest 2210 or other protrusion for placement of the hub orbattery.

FIG. 25 illustrates another embodiment of a wearable device 2200 in theform of a cap with a wearable garment 2208 in the form of a scarf thatmay contain or conceal a cable, a battery, and/or a hub. FIG. 26illustrates additional embodiments of a wearable device 2200 in the formof a helmet with a one-piece scarf 2208 or a two-piece scarf 2208-1.FIG. 27 illustrates an embodiment of a wearable device 2200 thatincludes a hood 2210 and a beanie 2212, which contains magnetometers2202, as well as a wearable garment 2208 that may contain a battery orhub.

The magnetic field measurement systems, wearable devices, and wearablesensor units described herein have been described with reference tomeasuring magnetic signals from the brain of a user. However, biologicalsignals from other areas of the body, as well as non-biological signals,can be measured using the systems, devices, and methods describedherein.

As mentioned above, a magnetic field generator design system may beconfigured to determine a configuration of one or more aspects ofmagnetic field generator 108. FIG. 28 illustrates an exemplary magneticfield generator design system 2800 (“design system”). Design system 2800may be implemented by a desktop computer, mobile device, server, and/orany other suitable computing device.

As shown, design system 2800 may include, without limitation, a storagefacility 2802 and a processing facility 2804 selectively andcommunicatively coupled to one another. Facilities 2802 and 2804 mayeach include or be implemented by hardware and/or software components(e.g., processors, memories, communication interfaces, instructionsstored in memory for execution by the processors, etc.).

Storage facility 2802 may maintain (e.g., store) executable data used byprocessing facility 2804 to perform one or more of the operationsdescribed herein. For example, storage facility 2802 may storeinstructions 206 that may be executed by processing facility 2804 toperform one or more of the operations described herein. Instructions2806 may be implemented by any suitable application, software, code,and/or other executable data instance. Storage facility 2802 may alsomaintain any data received, generated, managed, used, and/or transmittedby processing facility 2804.

Processing facility 2804 may be configured to perform (e.g., executeinstructions 2806 stored in storage facility 2802 to perform) variousoperations described herein.

As shown, design system 2800 may be communicatively coupled to a userinput device 2808 and a display device 2810. User input device 2808 maybe implemented by a keyboard, mouse, touch screen, track ball, joystick,voice recognition system, and/or any other device configured tofacilitate providing of user input to computing device 2800. Displaydevice 2810 may be implemented by a monitor, screen, printer, and/or anyother device configured to display output provided by computing device2800. In some examples, display device 2810 is integrated into a singleunit with computing device 2800.

In some examples design system 2800 may run a design algorithmconfigured to generate winding patterns of any one or more conductivewindings included in magnetic field generator 108. Additionally oralternatively, design system 2800 is configured to generate anarrangement of wearable sensor units 102 in a wearable device 2100and/or in magnetic field measurement system 100. Design system 2800 mayalso be configured to model magnetic fields generated by the generatedwinding patterns as well as ambient background magnetic fields. Anysuitable design algorithm and magnetic field models may be used as maysuit a particular implementation.

Design system 2800 may receive input specifying values of one or moreparameters associated with a magnetic field generator. Exemplaryparameters may include, without limitation, physical parameters (e.g.,identification of planes in a 3D space on which conductive windingsand/or wiring sets may be arranged; shapes, sizes, and/or dimensions ofsubstrates; locations of support posts, holes for screws, holes forlight transmission, magnetometers, and/or vapor cells; a shape of auser's head; etc.), wiring parameters (e.g., wire materials, wirethicknesses, distance between adjacent wires, etc.), driving parameters(e.g., maximum driving current and/or voltage values, power dissipation,etc.), magnetic field parameters (e.g., shape, size, and/or position ofthe magnetic field sensing region; predetermined threshold values forthe magnitude of ambient background magnetic fields at the magneticfield sensing region; gradient components of the compensation magneticfield; ambient background magnetic field sources, magnitude, andlocations; fringe magnetic field projection distances; predeterminedthreshold values for the magnitude of fringe magnetic fields at themagnetic field sensing region; etc.), and tolerance parameters (e.g.,tolerances for any of the above-listed parameters, manufacturing and/orassembly tolerances, etc.).

In some examples the one or more parameters may include variousmanufacturing errors (e.g., errors in wire widths, spacing betweenwires, alignment, etc.). By intentionally including manufacturing errorsin the input to design system 2800, design system 2800 may generatewinding patterns and configurations of a magnetic field generator thatare tolerant of manufacturing errors.

Design system 2800 may generate one or more magnetic field generatorconfigurations that satisfy the set of input parameters. For example,design system 2800 may generate winding patterns of conductive windings802, Bx′/By′ component conductive windings, and/or conductive windings1804. Additionally or alternatively, design system 2800 may generateconfigurations of substrates 902 and/or 1404. Additionally oralternatively, design system 2800 may generate configurations ofwearable device 2100 (e.g., winding patterns of counter-windings,locations and spacing of wearable sensor units 102, etc.).

Design system 2800 may model a compensation magnetic field produced byeach of the generated magnetic field generator configurations andambient background magnetic fields. Based on the models, design system2800 may output a set of magnetic field generator configurations thatproduce a modeled compensation magnetic field that actively shields amagnetic field sensing region from modeled ambient background magneticfields in accordance with user input criteria.

FIG. 29 shows an exemplary method 2900 of making a magnetic fieldgenerator. While FIG. 29 illustrates exemplary operations according toone embodiment, other embodiments may omit, add to, reorder, combine,and/or modify any of the steps shown in FIG. 29. One or more of theoperations shown in FIG. 29 may be performed by design system 2800, anycomponents included therein, and/or any implementation thereof.

In operation 2902, a magnetic field generator design system receivesinput specifying values of one or more parameters associated with amagnetic field generator. Operation 2902 may be performed in any of theways described herein.

In operation 2904, the magnetic field generator design system generatesone or more magnetic field generator configurations based on the one ormore parameters. Operation 2904 may be performed in any of the waysdescribed herein.

In operation 2906, the magnetic field generator design system models acompensation magnetic field produced by each of the generated magneticfield generator configurations and an ambient background magnetic field.Operation 2906 may be performed in any of the ways described herein.

In operation 2908, the magnetic field generator design system outputs aset of magnetic field generator configurations that produce a modeledcompensation magnetic field that actively shields a magnetic fieldsensing region included in each generated magnetic field generatorconfiguration from the modeled ambient background magnetic fields inaccordance with the one or more parameters. Operation 2908 may beperformed in any of the ways described herein.

FIG. 30 shows another exemplary method 3000 of making a magnetic fieldgenerator. While FIG. 30 illustrates exemplary operations according toone embodiment, other embodiments may omit, add to, reorder, combine,and/or modify any of the steps shown in FIG. 30.

In operation 3002, a first conductive winding is arranged on a firstplanar substrate. Operation 3002 may be performed in any of the waysdescribed herein.

In operation 3004, a second conductive winding is arranged on a secondplanar substrate. Operation 3004 may be performed in any of the waysdescribed herein.

In operation 3006, the second planar substrate is positioned opposite tothe first planar substrate with a gap therebetween and such that thefirst planar substrate is substantially parallel to the second planarsubstrate. Operation 3006 may be performed in any of the ways describedherein.

FIG. 31 shows another exemplary method 3100 of making a magnetic fieldgenerator. While FIG. 31 illustrates exemplary operations according toone embodiment, other embodiments may omit, add to, reorder, combine,and/or modify any of the steps shown in FIG. 31.

In operation 3102, a first conductive winding is arranged on a firstsurface of a first planar substrate. Operation 3102 may be performed inany of the ways described herein.

In operation 3104, a second conductive winding is arranged on a firstsurface of a second planar substrate. Operation 3104 may be performed inany of the ways described herein.

In operation 3106, a third conductive winding is arranged on a secondsurface of the first planar substrate. Operation 3106 may be performedin any of the ways described herein.

In operation 3108, a fourth conductive winding is arranged on a secondsurface of the second planar substrate. Operation 3108 may be performedin any of the ways described herein.

In operation 3110, the second planar substrate is positioned opposite tothe first planar substrate with a gap therebetween and such that thefirst planar substrate is substantially parallel to the second planarsubstrate. Operation 3110 may be performed in any of the ways describedherein.

FIG. 32 shows another exemplary method 3200 of making a magnetic fieldgenerator. While FIG. 32 illustrates exemplary operations according toone embodiment, other embodiments may omit, add to, reorder, combine,and/or modify any of the steps shown in FIG. 32.

In operation 3202, a first wiring set is arranged on a first planarsubstrate such that wires in the first wiring set extend in a firstdirection. Operation 3202 may be performed in any of the ways describedherein.

In operation 3204, a second wiring set is arranged on a second planarsubstrate such that wires in the second wiring set extend in the firstdirection. Operation 3204 may be performed in any of the ways describedherein.

In operation 3206, one or more interconnects are arranged on the firstplanar substrate such that a first surface of the one or moreinterconnects electrically connects with ends of the wires in the firstwiring set. Operation 3206 may be performed in any of the ways describedherein.

In operation 3208, the second planar substrate is positioned on a secondsurface of the one or more interconnects such that the first planarsubstrate is substantially parallel to the second planar substrate andsuch that the second surface of the one or more interconnectselectrically connects with ends of wires in the second wiring set toform a continuous electrical path through the first wiring set, thesecond wiring set, and the one or more interconnects. Operation 3208 maybe performed in any of the ways described herein.

The methods described above may be combined and/or modified in anysuitable way. For example, any of the methods described above may becombined, repeated, and/or modified to produce any of the magnetic fieldgenerators described herein. Moreover, any steps described above inmethod 3000, 3100, and/or 3200 may be performed by any suitable PCBmanufacturing process.

In some examples, a non-transitory computer-readable medium storingcomputer-readable instructions may be provided in accordance with theprinciples described herein. The instructions, when executed by aprocessor of a computing device, may direct the processor and/orcomputing device to perform one or more operations, including one ormore of the operations described herein. Such instructions may be storedand/or transmitted using any of a variety of known computer-readablemedia.

A non-transitory computer-readable medium as referred to herein mayinclude any non-transitory storage medium that participates in providingdata (e.g., instructions) that may be read and/or executed by acomputing device (e.g., by a processor of a computing device). Forexample, a non-transitory computer-readable medium may include, but isnot limited to, any combination of non-volatile storage media and/orvolatile storage media. Exemplary non-volatile storage media include,but are not limited to, read-only memory, flash memory, a solid-statedrive, a magnetic storage device (e.g. a hard disk, a floppy disk,magnetic tape, etc.), ferroelectric random-access memory (“RAM”), and anoptical disc (e.g., a compact disc, a digital video disc, a Blu-raydisc, etc.). Exemplary volatile storage media include, but are notlimited to, RAM (e.g., dynamic RAM).

FIG. 33 illustrates an exemplary computing device 3310 that may bespecifically configured to perform one or more of the processesdescribed herein. Any of the systems, units, computing devices, and/orother components described herein may be implemented by computing device3310.

As shown in FIG. 33, computing device 3310 may include a communicationinterface 3312, a processor 3314, a storage device 3316, and aninput/output (“I/O”) module 3318 communicatively connected one toanother via a communication infrastructure 3320. While an exemplarycomputing device 3310 is shown in FIG. 33, the components illustrated inFIG. 33 are not intended to be limiting. Additional or alternativecomponents may be used in other embodiments. Components of computingdevice 3310 shown in FIG. 33 will now be described in additional detail.

Communication interface 3312 may be configured to communicate with oneor more computing devices. Examples of communication interface 3312include, without limitation, a wired network interface (such as anetwork interface card), a wireless network interface (such as awireless network interface card), a modem, an audio/video connection,and any other suitable interface.

Processor 3314 generally represents any type or form of processing unitcapable of processing data and/or interpreting, executing, and/ordirecting execution of one or more of the instructions, processes,and/or operations described herein. Processor 3314 may performoperations by executing computer-executable instructions 3322 (e.g., anapplication, software, code, and/or other executable data instance)stored in storage device 3316.

Storage device 3316 may include one or more data storage media, devices,or configurations and may employ any type, form, and combination of datastorage media and/or device. For example, storage device 3316 mayinclude, but is not limited to, any combination of the non-volatilemedia and/or volatile media described herein. Electronic data, includingdata described herein, may be temporarily and/or permanently stored instorage device 3316. For example, data representative ofcomputer-executable instructions 3322 configured to direct processor3314 to perform any of the operations described herein may be storedwithin storage device 3316. In some examples, data may be arranged inone or more databases residing within storage device 3316.

I/O module 3318 may include one or more I/O modules configured toreceive user input and provide user output. I/O module 3318 may includeany hardware, firmware, software, or combination thereof supportive ofinput and output capabilities. For example, I/O module 3318 may includehardware and/or software for capturing user input, including, but notlimited to, a keyboard or keypad, a touchscreen component (e.g.,touchscreen display), a receiver (e.g., an RF or infrared receiver),motion sensors, and/or one or more input buttons.

I/O module 3318 may include one or more devices for presenting output toa user, including, but not limited to, a graphics engine, a display(e.g., a display screen), one or more output drivers (e.g., displaydrivers), one or more audio speakers, and one or more audio drivers. Incertain embodiments, I/O module 3318 is configured to provide graphicaldata to a display for presentation to a user. The graphical data may berepresentative of one or more graphical user interfaces and/or any othergraphical content as may serve a particular implementation.

In the preceding description, various exemplary embodiments have beendescribed with reference to the accompanying drawings. It will, however,be evident that various modifications and changes may be made thereto,and additional embodiments may be implemented, without departing fromthe scope of the invention as set forth in the claims that follow. Forexample, certain features of one embodiment described herein may becombined with or substituted for features of another embodimentdescribed herein. The description and drawings are accordingly to beregarded in an illustrative rather than a restrictive sense.

1. A magnetic field generator comprising: a first planar substrate; asecond planar substrate positioned opposite to the first planarsubstrate and separated from the first planar substrate by a gap, afirst wiring set disposed on the first planar substrate, a second wiringset disposed on the second planar substrate, and one or moreinterconnects positioned between the first planar substrate and thesecond planar substrate and that electrically connect the first wiringset with the second wiring set to form a first continuous electricalpath, wherein the first continuous electrical path forms a firstconductive winding configured to generate, when supplied with a firstdrive current, a first component of a compensation magnetic fieldconfigured to actively shield a magnetic field sensing region located inthe gap from ambient background magnetic fields along a first axis thatis substantially parallel to the first planar substrate and the secondplanar substrate.
 2. The magnetic field generator of claim 1, whereinthe first component of the compensation magnetic field is configured toactively shield the magnetic field sensing region by reducing orcanceling a first component of the ambient background magnetic field,the first component of the ambient background magnetic field being alongthe first axis.
 3. The magnetic field generator of claim 2, wherein thefirst component of the compensation magnetic field is substantiallyequal and opposite to the first component of the ambient backgroundmagnetic field.
 4. The magnetic field generator of claim 1, wherein theone or more interconnects comprises an elastomeric connector that isanisotropically conductive.
 5. The magnetic field generator of claim 1,wherein the elastomeric connector is configured to maintain a minimumspacing between the first planar substrate and the second planarsubstrate.
 6. The magnetic field generator of claim 1, wherein each ofthe first planar substrate and the second planar substrate comprises aprinted circuit board.
 7. The magnetic field generator of claim 1,wherein a winding pattern of the first conductive winding includes afirst counter-winding configured to reduce a spatial extent of a firstfringe magnetic field generated by the first conductive winding.
 8. Themagnetic field generator of claim 1, further comprising: a firstgradient wiring and a second gradient disposed on the first planarsubstrate; and a third gradient wiring and a fourth gradient wiringdisposed on the second planar substrate; wherein the one or moreinterconnects electrically connect the first gradient wiring with thethird gradient wiring to form a first additional continuous electricalpath, the additional continuous electrical path forming a first gradientconductive winding, the one or more interconnects electrically connectthe second gradient wiring with the fourth gradient wiring to form asecond additional continuous electrical path, the second additionalcontinuous electrical path forming a second gradient conductive winding,and the first gradient conductive winding and the second gradientconductive winding are configured to generate, when supplied withdifferent drive currents, a first gradient component of the compensationmagnetic field configured to actively shield the magnetic field sensingregion from ambient background magnetic fields that linearly vary alongthe first axis.
 9. The magnetic field generator of claim 1, furthercomprising: a third wiring set disposed on the first planar substrate, afourth wiring set disposed on the second planar substrate, and the oneor more interconnects electrically connect the third wiring set with thefourth wiring set to form a second continuous electrical path, whereinthe second continuous electrical path forms a second conductive windingconfigured to generate, when supplied with a second drive current, asecond component of the compensation magnetic field configured toactively shield the magnetic field sensing region from the ambientbackground magnetic fields along a second axis that is substantiallyparallel to the first planar substrate and the second planar substrateand orthogonal to the first axis.
 10. The magnetic field generator ofclaim 9, wherein the second component of the compensation magnetic fieldis configured to actively shield the magnetic field sensing region byreducing or canceling a second component of the ambient backgroundmagnetic fields, the second component of the ambient background magneticfields being along the second axis.
 11. The magnetic field generator ofclaim 10, wherein the second component of the compensation magneticfield is substantially equal and opposite to the second component of theambient background magnetic fields.
 12. The magnetic field generator ofclaim 9, wherein: the first wiring set and the third wiring set areformed on a first surface of the first planar substrate and areelectrically insulated from one another, and the second wiring set andthe fourth wiring set are formed on a first surface of the second planarsubstrate and are electrically insulated from one another.
 13. Themagnetic field generator of claim 9, wherein: the first wiring set isformed on a first surface of the first planar substrate, the thirdwiring set is formed on a second surface of the first planar substrate,the second wiring set is formed on a first surface of the second planarsubstrate, and the fourth wiring set is formed on a second surface onthe second planar substrate.
 14. The magnetic field generator of claim9, further comprising: a first gradient wiring and a second gradientdisposed on the first planar substrate; and a third gradient wiring anda fourth gradient wiring disposed on the second planar substrate;wherein the one or more interconnects electrically connect the firstgradient wiring with the third gradient wiring to form a firstadditional continuous electrical path, the additional continuouselectrical path forming a first gradient conductive winding, the one ormore interconnects electrically connect the second gradient wiring withthe fourth gradient wiring to form a second additional continuouselectrical path, the second additional continuous electrical pathforming a second gradient conductive winding, and the first gradientconductive winding and the second gradient conductive winding areconfigured to generate, when supplied with different drive currents, afirst gradient component of the compensation magnetic field configuredto actively shield the magnetic field sensing region from ambientbackground magnetic fields that linearly vary along the first axis. 15.The magnetic field generator of claim 14, further comprising: a fifthgradient wiring and a sixth gradient disposed on the first planarsubstrate; and a seventh gradient wiring and an eighth gradient wiringdisposed on the second planar substrate; wherein the one or moreinterconnects electrically connect the fifth gradient wiring with theseventh gradient wiring to form a third additional continuous electricalpath, the third additional continuous electrical path forming a thirdgradient conductive winding, the one or more interconnects electricallyconnect the sixth gradient wiring with the eighth gradient wiring toform a fourth additional continuous electrical path, the fourthadditional continuous electrical path forming a fourth gradientconductive winding, and the third gradient conductive winding and thefourth gradient conductive winding are configured to generate, whensupplied with different drive currents, a second gradient component ofthe compensation magnetic field configured to actively shield themagnetic field sensing region from ambient background magnetic fieldsthat linearly vary along the second axis.
 16. The magnetic fieldgenerator of claim 15, further comprising: a fifth gradient conductivewinding disposed on the first planar substrate; and a sixth gradientconductive winding disposed on the second planar substrate; wherein thefifth gradient conductive winding and the sixth gradient conductivewinding are configured to generate, when supplied with different drivecurrents, a combination gradient component.
 17. The magnetic fieldgenerator of claim 1, further comprising: a plurality of additionalconductive windings comprising: a first additional conductive windingarranged in a first plane, and a second additional conductive windingarranged in a second plane that is substantially parallel to the firstplane, wherein the plurality of additional conductive windings areconfigured to generate, when supplied with a drive current, a thirdcomponent of the compensation magnetic field, the third component of thecompensation magnetic field being configured to actively shield themagnetic field sensing region from the ambient background magneticfields along a third axis that is substantially orthogonal to the firstplane and the second plane.
 18. The magnetic field generator of claim17, wherein the third component of the compensation magnetic field isconfigured to actively shield the magnetic field sensing region byreducing or canceling a third component of the ambient backgroundmagnetic fields, the third component of the ambient background magneticfields being along the third axis.
 19. The magnetic field generator ofclaim 18, wherein the third component of the compensation magnetic fieldis substantially equal and opposite to the third component of theambient background magnetic fields.
 20. The magnetic field generator ofclaim 17, wherein: the first additional conductive winding is arrangedon a surface of the first planar substrate, and the second additionalconductive winding is arranged on a surface of the second planarsubstrate.
 21. The magnetic field generator of claim 17, furthercomprising a third planar substrate and a fourth planar substrate,wherein: the first additional conductive winding is arranged on asurface of the third planar substrate, and the second additionalconductive winding is arranged on a surface of the fourth planarsubstrate.
 22. The magnetic field generator of claim 17, wherein: theplurality of additional conductive windings further comprises: a thirdadditional conductive winding arranged in a third plane, and a fourthadditional conductive winding arranged in a fourth plane, and the thirdplane and the fourth plane are substantially parallel to the first planeand the second plane.
 23. The magnetic field generator of claim 22,further comprising a third planar substrate and a fourth planarsubstrate, wherein: the first additional conductive winding is arrangedon a first surface of the third planar substrate, the first surface ofthe third planar substrate facing away from the magnetic field sensingregion, the second additional conductive winding is arranged on a firstsurface of the fourth planar substrate, the first surface of the fourthplanar substrate facing away from the magnetic field sensing region, thethird additional conductive winding is arranged on a second surface ofthe third planar substrate, the second surface of the third planarsubstrate facing the magnetic field sensing region, and the fourthadditional conductive winding is arranged on a second surface of thefourth planar substrate, the second surface of the fourth planarsubstrate facing the magnetic field sensing region. 24-90. (canceled)